But it took billionaire Warren Buffett several decades to start
donating his massive fortune — a decision his late first wife
Susan grappled with, according to the new HBO documentary
"Becoming Warren Buffett."

"You don't have to be particularly smart, you just have to be
patient. Susie didn't want to wait as much as I did — she never
quite appreciated compounding like I did."

In 1977, when their three children were grown, Susan left the
family's home in Omaha to focus on her charitable work.

"My mom moved to San Francisco and I think one of the reasons it
was so important for her to leave Omaha was because she just left
like she was kinda trapped in this environment, that everybody
knew who she was, and she couldn't have her own identity," said
the couple's younger son, Peter.

"[My dad] knew that there was something [my mom] needed to do,
and that she really recognized that the money gave us all, and
her, a choice in a lot of ways that a lot of people didn't have,"
their older son, Howard, said.

Susan chose to dedicate her time and money to charity, while
Buffett continued working and growing his fortune (the two
remained close friends, and legally married, until her death in
2004).

"It was a time where Warren was criticized. There was this very,
very rich man who was getting richer every year, and really
wasn't giving any money away and there was terrific criticism by
some people, which Warren never said anything about," said Sandy
Gottesman, a friend of Buffett's, as well as an investor and
early backer of Berkshire Hathaway.

Susan and Warren Buffett
remained close friends, and legally married, until her death in
2004."Becoming Warren
Buffett"/HBO

"That is a disagreement we have," Susan said in an interview
recorded before her death, which is included in the documentary.
"I run a foundation now. I think we should be giving more money
away. But I understand why we don't — because it's business."

She continued: "To me, the crux of it is: It wasn't the money
itself. You can see that in the way he lives. He doesn't buy huge
paintings or build big houses or anything like that. It's all
mental with him, and the money is his scorecard. He used to say
to me, 'Everybody can read what I read. It's a level playing
field.' And he loves that because he's competitive. So he's
sitting there all by himself in his office reading these things
that everybody else can read. But, he loves the idea that he's
going to win."

In 2006, two years after Susan's death, Buffett ramped up his
giving, promising to gradually donate all of his Berkshire
Hathaway stock to philanthropy.

In 2010, he teamed up with fellow billionaires and close friends
Bill and Melinda Gates to start the Giving Pledge, vowing to
donate 99% of his fortune to charitable causes in his lifetime.

He said in his 2010 Giving
Pledge letter: "To date, 20% of my shares have been
distributed (including shares given by my late wife, Susan
Buffett). I will continue to annually distribute about 4% of the
shares I retain ... this pledge will leave my lifestyle untouched
and that of my children as well. ... And I will continue to live
in a manner that gives me everything that I could possibly want
in life."